A keystone species

The wolf is often called a keystone species. A keystone species is one whose abundance is relatively low but whose effect on its community or ecosystem is relatively large (Power et al., 1996 cited in Estes, 1996). Computer models have predicted that wolves in YNP may reduce ungulate numbers by 5%-30% and also decrease fluctuations in ungulate numbers, without having devastating affects on these populations (Schullery, 1996). There has been a steady increase in deer populations in North America, which is in part a response to the extirpation of large predators, especially wolves (Estes, 1996). An increase in the gray wolf populations in northern Montana has seen a concurrent decrease in elk and white-tailed deer density (Estes, 1996).

Reintroducing a top carnivore to an ecosystem that has been without this predator for many years is going to result in reduced prey populations, specifically ungulate populations. The concern is whether this reduction is going to threaten prey populations because the predation is too intense. The significance of the decreased populations depends on other conditions, including the initial density of prey populations, distribution, other population limiting factors such as hunting, disease, food, and predator avoidance capabilities. Lariviere et al. (2000) concluded that ecosystems with multiple-prey base are able to sustain higher densities of wolves than systems with a single prey. There exists a constant pressure between predator and prey-predators kill enough to eat, but enough prey escape to reproduce (Mech et al., 1998). It is a force that results in stable and abundant populations of predators and prey in the absence of human disturbance (Mech et al., 1998).

As a species, wolves are well able to adapt to their environment (Steinhart, 1995), and therefore their behavior and consumption are sensitive to the abundance of prey. Predator and prey populations have exhibited long term oscillations on Isle Royale (Peterson, 1984). In Quebec, moose have a strong influence on wolf density. Their relationship is exponential, such that as moose density increases, wolf density increases, especially when moose numbers are 3 per 10 square kilometers (Lariviere, 2000). The ability of wolves to adapt was evident in this study when moose densities were extremely low in this single ungulate prey system, and wolf populations persisted. Wolves adapted to the changing conditions and still thrived when moose density dropped to 0.6 moose per 10 square kilometers.

Wolves are smart hunters and likely turned towards smaller prey such as the high density of beavers (Larieviere, 2000). Of course the effect of wolf predation varies depending on the different prey. Studies on wolf populations in Poland looked at the significance of wolf predation on specific ungulate populations. Over the course of a year, wolves take 20% and 16% of wild boar and red deer populations, respectively (Glowacinski and Profus, 1996). This impact was most significant because the bulk of the biomass taken was young ungulates, less than one year old. This means that prey populations lose young members and fewer animals will reach reproductive age, so the population growth is somewhat limited. However, the final results from this study of Poland wolf predation concluded that this loss of natural population growth does not seem sufficient to threaten the reproduction and stability of ungulate populations (Glowacinski and Profus, 1996).

With the reintroduction of wolves in North America a reduction in ungulate density is expected, however this does not mean that wolf predation will exterminate ungulate populations. The ability of wolves to adjust to varying prey density prevents extermination of less common prey. Prey populations will be regulated by the reintroduction of this predator-prey relationship, but perhaps this interaction will serve to reestablish natural balances in the system and limit fluctuating ungulate populations.

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